Absolutely Rare – Blobfish

Wikipedia:The blobfish is a deep sea fish…[i]nhabiting the deep waters off the coasts of mainland Australia and Tasmania, it is rarely seen by humans.
Blobfish live at depths between 600–1,200 m (2,000–3,900 ft) where the pressure is several dozen times higher than at sea level, which would likely make gas bladders inefficient for maintaining buoyancy.
Instead, the flesh of the blobfish is primarily a gelatinous mass with a density slightly less than water; this allows the fish to float above the sea floor without expending energy on swimming.